Operation Retribution (German: Unternehmen Strafgericht) also known as Operation Punishment, was the codename used for the April 1941 Germanbombing of Belgrade, the capital of the Kingdom of Yugoslavia, in the first days of the German-led Axisinvasion of Yugoslavia. The operation commenced on 6 April and concluded on 7 or 8 April, resulting in paralysis of Yugoslav civilian and military command and control, widespread destruction largely in the centre of the city, and significant civilian casualties. The bombing of Belgrade was preceded by the commencement of the ground invasion a few hours earlier, and also coincided with air attacks on a large number of Royal Yugoslav Air Force airfields and other strategic targets across Yugoslavia. The invasion resulted in the surrender of Yugoslav forces on 17 April.

Further pressure was applied by Hitler on 4 March 1941, when the Yugoslav Regent, Prince Paul, visited Berchtesgaden, but Prince Paul delayed a decision.[3] On 6 March, the Royal Yugoslav Air Force (Serbo-Croatian: Vazduhoplovstvo Vojske Kraljevine Jugoslavije, VVKJ) was secretly mobilised,[4] and on the following day, British troops began landing in Greece to bolster the defences of their Balkan ally against the Italians.[5] The VVKJ began dispersing to auxiliary airfields on 12 March, and this dispersal was completed by 20 March.[4] Hitler, wanting to secure the southern flank of his impending invasion of the Soviet Union, demanded that Yugoslavia sign the Pact, and the Yugoslav government eventually complied on 25 March 1941.[6] Two days later a military coup d'état was carried out by a group of VVKJ and Yugoslav Royal Guard officers, led by VVKJ commander Brigadier GeneralBorivoje Mirković.[7] Prince Paul was deposed and replaced by the 17-year-old King Peter II who was declared to be of age.[8]

On the same day as the Yugoslav coup d'état, Hitler issued Directive 25, which stated that the coup had changed the political situation in the Balkans. He ordered that "even if Yugoslavia at first should give declarations of loyalty, she must be considered as a foe and therefore must be destroyed as quickly as possible."[9] After the coup, German reconnaissance aircraft frequently violated Yugoslav airspace, and VVKJ fighter aircraft were on constant alert. The German incursions showed that the Yugoslav ground observation post network and supporting radio communications were inadequate.[4]

The bomb-damaged Old Palace in central Belgrade. The royal palaces located in the city centre and the southern suburb of Dedinje were among the targets of the Luftwaffe during the first wave of bombing on 6 April 1941.

Hitler decided that Belgrade would be bombed in "retribution" for the coup against the government that had signed the Pact. In order to carry out Hitler's orders, on 27 and 28 March 1941 ReichsmarschallHermann Göring transferred about 500 fighter and bomber aircraft from France and northern Germany. The commander of Luftflotte IV, Generaloberst (General) Alexander Löhr, allocated these aircraft to attack the Yugoslav capital in waves by day and night. Löhr issued his orders for the bombing on 31 March, but the decision to bomb Belgrade was not confirmed by Hitler until 5 April.[10] Although Hitler ordered the general destruction of Belgrade, Löhr replaced these general directions with specific military objectives at the last minute.[11] On 3 April, MajorVladimir Kren of the VVKJ defected to the Germans, flying a Potez 25 aircraft to Graz in the Third Reich, and handing over the locations of many of the dispersal airfields as well as codes used by the VVKJ, which had to be quickly changed. On the afternoon of 5 May, a British colonel visited Mirković at the VVKJ base at Zemun and confirmed that the attack on Belgrade would commence at 06:30 the following morning.[4]

Yugoslav anti-aircraft defences caused a false alarm when they reported the approach of an air raid from the direction of Romania at 03:00, but listening posts on the Romanian border had actually heard the aircraft engines of the Romanian-based Fliegerführer Arad warming up well before they took off. The VVKJ's 51st Fighter Group at Zemun had been alerted before dawn, and when reports began to be received about Luftwaffe attacks on VVKJ airfields, the first patrol was sent into the air. At first, no aircraft could be seen approaching Belgrade.[13]

The first wave closed on Belgrade at 06:45, and consisted of 74 Junkers Ju 87Stuka divebombers and 160 Heinkel He 111medium bombers and Dornier Do 17light bombers between 8,000–10,000 feet (2,400–3,000 m). They were escorted by Messerschmitt Bf 110heavy fighters at 11,000–12,000 feet (3,400–3,700 m) and 100 Messerschmitt Bf 109E fighters at 15,000 feet (4,600 m).[14] The whole of the Yugoslav 6th Fighter Brigade, consisting of the 51st Fighter Group at Zemun and the 32nd Fighter Group at Prnjavor, totalling 29 Messerschmitt Bf 109Es and 5 Rogožarski IK-3s, were scrambled to intercept the Germans.[15] The Yugoslavs were quickly engaged by escorting Messerschmitt Bf 109Es from Jagdgeschwader 77 (JG 77). Just as the first wave was departing, Hawker Hurricane Mk1s of the 52nd Group of the 2nd Fighter Brigade based at Knić arrived over Belgrade and engaged some divebombers, claiming one Stuka shot down. During the first attack, the Yugoslavs claimed fifteen German aircraft shot down, lost five of their own, with more than six badly damaged. The pilots of JG 77 claimed ten Yugoslav machines shot down and another six destroyed on the ground.[16] On his return to base, the commander of the 51st Fighter Group was relieved of his command for failure to take action.[17]

The second wave arrived over Belgrade about 10:00, consisting of fifty-seven Junkers Ju 87 divebombers and thirty Messerschmitt Bf 109Es fighters. They were met by fifteen of the remaining fighters from the 6th Fighter Brigade. This time the Yugoslavs claimed two divebombers forced down, and one Bf 109E shot down. A patrol of Bf 109Es from the Yugoslav 31st Fighter Group based at Kragujevac, acting without orders of their group commander, followed the Germans as they returned to their bases and claimed two divebombers shot down for the loss of both Yugoslav aircraft.[17]

Two further attacks were made on Belgrade by the Germans on the first day of the invasion. The third wave struck at 14:00, consisting of ninety-four twin-engined bombers flying from airfields near Vienna, escorted by sixty fighters. This attack was confronted by eighteen fighters of the 6th Fighter Regiment, who claimed four German aircraft shot down. The fourth attack of the day approached Belgrade at 16:00, comprising ninety-seven divebombers and sixty fighters.[17]

The German groups attacking Belgrade claimed a total of nineteen Yugoslav Bf 109E fighters and four unidentified aircraft destroyed on 6 April. Actual Yugoslav aircraft losses on the first day were ten shot down and fifteen damaged. The Yugoslavs claimed they had shot down twenty-two German aircraft and forced two more to land. The Germans lost significantly less aircraft than claimed by the Yugoslavs, a total of twelve aircraft; two Do 17Z light bombers, five Bf 110 heavy fighters, four Ju 87 divebombers and one Bf 109E fighter.[17] One Luftwaffe pilot who claimed his first victory over Belgrade on 6 April was OberleutnantGerhard Koall of JG 54,[17] who went on to be credited with thirty-seven victories and was awarded the Knight's Cross of the Iron Cross in 1944.[18]

In total, bombers and dive-bombers dropped 215–360 long tons (241–403 short tons) of bombs and incendiaries on the capital.[19][20]

The weak Royal Yugoslav Air Force and inadequate anti-aircraft defences of Belgrade briefly attempted to meet the overwhelming Luftwaffe assault, but were eliminated as threats during the first wave of the attack. Sources vary regarding the success achieved by the defenders. A U.S. Army study first published in 1953 states that the Luftwaffe lost two fighter aircraft, and shot down 20 Yugoslav aircraft and destroyed 44 on the ground,[21] whereas other sources state that the Yugoslavs shot down 40 German aircraft over the two-day air battle.[19] Dive-bombers in subsequent waves were able to operate at rooftop altitude.[21]

According to the historian Professor Stevan K. Pavlowitch, the bombing of Belgrade lasted for three days,[22] other sources state the air battle over Belgrade lasted just two days owing to poor flying weather on 8 April.[19]

The most important cultural institution that was destroyed was the National Library of Serbia, which was hit by bombs and gutted by fire. Hundreds of thousands of volumes, rare books, maps, and medieval manuscripts were destroyed.[23]

No. 37 Squadron of the Royal Air Force conducted two bombing raids on Sofia, the capital of Bulgaria, in retaliation for the bombing of Belgrade. Operating Vickers Wellington bombers flying from an airfield in Greece, the squadron conducted raids on 6–7 April and 12–13 April, dropping a total of 30 long tons (34 short tons) of high-explosive bombs on railway targets and nearby residential areas. These raids were carried out despite the fact that Britain was not at war with Bulgaria until 12 December 1941.[24]

The bombing of Belgrade paralysed communications between the Yugoslav military and its headquarters, and contributed decisively to the rapid collapse of Yugoslav resistance.[11]

Monument to the Royal Yugoslav Air Force defenders of Belgrade, located in New Belgrade

Civilian casualties were significant, but sources vary widely from 1,500 to 17,000 killed.[25] According to the journalist William Stevenson, around 24,000 corpses were recovered from the ruins, and many were never found.[26] The official casualty figure soon after the bombing was 2,271 killed, but other sources use 5,000[27] or 10,000, with later Yugoslav estimates ranging even higher.[28] In contrast, Professor Jozo Tomasevich states that the higher estimates were downgraded following "careful postwar investigations", and indicates that a figure between 3,000 and 4,000 is more realistic.[29]

Following the Yugoslav capitulation, Luftwaffe engineers conducted a bomb damage assessment in Belgrade. The report stated that 218.5 metric tons (215.0 long tons; 240.9 short tons) of bombs were dropped, with 10–14 percent being incendiaries. It listed all the targets of the bombing, which included: the royal palace, the war ministry, military headquarters, the central post office, the telegraph office, passenger and goods railway stations, power stations and barracks. It also mentioned that seven aerial mines were dropped, and that areas in the centre and northwest of the city had been destroyed, comprising 20–25 percent of its total area. Some aspects of the bombing remain unexplained, particularly the use of the aerial mines.[11] In contrast to this report, Pavlowitch states that almost 50 percent of housing in Belgrade was destroyed.[30] After the invasion, the Germans forced 3,500–4,000 Jews to collect rubble that was caused by the bombing.[31]

Löhr was captured by the Yugoslav Partisans on 9 May 1945, escaped, and was recaptured on 13 May. He was intensively interrogated, after which he was tried before a Yugoslav military court on a number of war crimes charges, one of which related to his command of Luftflotte IV during Operation Retribution. He was convicted, sentenced to death and executed.[32]